The present invention relates to an electric power conversion apparatus having a noise reduction device for reducing a common mode noise and a normal mode noise caused by a switching device of an electric power conversion apparatus when operating an alternate current (as referred to AC from hereon) motor.
FIG. 5 is a circuit diagram of a conventional noise reduction device applied to a system, which drives a three-phase induction motor via a three-phase converter. The noise reduction device described in FIG. 5 is substantially the same with the noise reduction device disclosed in Japanese Unexamined Laid Open Patent Application No. H09-266677.
Shown in FIG. 5 are a single-phase AC power supply 1; a single-phase rectifying bridge circuit 2 as a converter; a three-phase inverter circuit 3 including semiconductor switching devices Q1 through Q6, such as IGBT (Insulated Gate Bipolar Transistor), and diodes connected in opposite parallel to the respective semiconductor switching devices; a three-phase induction motor 4 as a load of the inverter circuit 3; a noise current detector 5, such as a zero-phase current transformer formed of a ring core 5a, a pair of primary windings 5b and 5c, and a secondary winding 5d; a noise-compensation-current supply circuit 6 connected to both ends of the secondary winding 5d; and a Direct Current (as referred to DC from hereon) smoothing capacitor C0 connected to a DC intermediate circuit between the rectifying circuit 2 and the inverter circuit 3. The polarity of each winding of the noise current detector 5 is set as shown in FIG. 5. The rectifying circuit 2, the DC smoothing capacitor C0, and the inverter circuit 3 constitute an electric power conversion apparatus.
The noise-compensation-current supply circuit 6 includes a NPN (Negative-Positive-Negative) transistor Tr1, a PNP (Positive-Negative-Positive) transistor Tr2, and a coupling capacitor C1 for cutting the DC component. Filter capacitors C2 and C3 are connected to both terminals of the AC power supply 1. Both ends of the secondary winding 5d are connected to the bases and the emitters of the transistors Tr1 and Tr2 constituting the noise-compensation-current supply circuit 6. The collector of the transistor Tr1 is connected to the positive terminal of the ecapacitor C0, and the collector of the transistor Tr2 to the negative terminal of the capacitor C0.
The frame of the induction motor 4 is grounded. The emitters of the transistors Tr1 and Tr2 are connected to a grounding point G via a coupling capacitor C1. The mutual connection point of the capacitors C2 and C3 is also connected to the grounding point G. In FIG. 5, the switching devices Q1 through Q6 of the inverter circuit 3 are controlled by PWM (Pulse Code Modulation), which is omitted from FIG. 5.
The operations of the conventional noise reduction device will be described below. The switching devices Q1 through Q6 of the inverter circuit 3 are controlled to switch on and off by the PWM pulses. The induction motor 4 is driven by the output of the inverter circuit 3. Since electrostatic capacitance (floating capacitance) C exists between the windings of the induction motor 4 and the grounding point G as shown by the broken lines in FIG. 5, a leakage current pulse (common mode noise current) IC flows through the electrostatic capacitance C whenever a voltage pulse is applied form the inverter circuit 3 to the induction motor 4. Since the noise current flowing straight through the grounding point G causes an electric shock and malfunction of the ground breaker, the noise current needs to be eliminated.
The noise current detector 5 detects the noise current (zero-phase current component) from the difference of the currents iCxe2x80x2 flowing through a pair of power supply lines of the DC intermediate current. When a noise current is detected, the noise current detector 5 makes a detection current iB1 flow through the secondary winding 5d. The detection current iB1 drives the transistors Tr1 or Tr2.
The detection current iB1, which has flowed into the base of the transistor Tr1 or Tr2, is amplified by the transistor Tr1 or Tr2, causing a current ic1. The transistors Tr1 and Tr2 switches on and off in opposite to each other such that when the transistor Tr1 is ON, the transistor Tr2 is OFF, and, when the transistor Tr1 is OFF, the transistor Tr2 is ON.
When the noise current ic flows in the direction indicated by the arrow in FIG. 5, the current iB1 caused by the current iCxe2x80x2 flowing through the primary windings 5b and 5c flows through the secondary winding 5d. The current iB1 switches on the transistor Tr2, and the noise compensation current ic1 circulates from the capacitor C0 to the capacitor C0 via any of the switching devices on the upper arm of the inverter circuit 3, the electrostatic capacitance C of the induction motor 4, the coupling capacitor C1, and the transistor Tr2.
Since most of the noise current iC flows as the current iC1, the current iCxe2x80x2 (=iCxe2x88x92iC1) flowing to the output side of the rectifying circuit 2 is reduced, and the noise voltage (the noise voltage at the AC input side terminal of the rectifying circuit 2) is also reduced.
Since the direction of the current iB1 flowing through the secondary winding 5d becomes opposite when the direction of the noise current iC is opposite, the transistor Tr1 is switched on. Therefore, the noise compensation current iC1 circulates from the capacitor C0 to the capacitor C0 via the transistor Tr1, the coupling capacitor C1, the electrostatic capacitance of the induction motor 4, and anyone of the switching devices on the lower arm of the inverter circuit 3. Since most of the noise current iC flows as the iC1 in this case as well, the current iCxe2x80x2 (=iCxe2x88x92iC1) is reduced, and the noise voltage is also reduced.
Since the transistors Tr1 and Tr2 constituting the noise-compensation-current supply circuit 6 are connected via the respective collectors thereof to the smoothing capacitor C0, it is required that the breakdown voltages of the transistors Tr1 and Tr2 be high enough to endure the DC voltage of the inverter circuit 3.
In the general purpose inverter, the AC input voltage (the effective value) thereof is 200 V, and the DC voltage (DC intermediate voltage) is around 500 V. When the AC input voltage thereof is 400 V, the DC voltage is around 1000 V. Therefore, it is necessary for the transistors Tr1 and Tr2 to exhibit a breakdown voltage high enough to endure these DC voltages.
However, since commercially available transistors with the breakdown voltage of 500 V operate less than half speed as that of the transistor with the breakdown voltage of 300 V, the transistor with the breakdown voltage of 500 V is not so effective to reduce the noise current.
Especially in the high frequency range, wherein the operating frequency of the inverter exceeds 1 MHz, the transistors constituting the noise-compensation-current supply circuit 6 sometimes can not catch up with such a high speed. Sometimes, the transistors constituting the noise-compensation-current supply circuit 6 operate in the opposite polarity of the noise current iC, resulting in amplifying noise voltage in the high frequency range.
To obviate this problem, it is necessary to employ a high frequency filter to cut the high frequency noises in addition to the filter capacitors C2 and C3. The additional high frequency filter enlarges the electric power conversion apparatus and increases the cost of the apparatus.
It is an object of the invention to provide a noise reduction device, which can use elements with lower breakdown voltage than the DC voltage of the inverter, and an electric power conversion apparatus with the noise reduction device, as the current control devices of the noise-compensation-current supply circuit.
It is another object of the invention to provide a noise reduction device, which prevents high frequency noises from causing and minimizes the high frequency filter, and the entire electric power conversion apparatus with the noise reduction device when the operating frequency of the electric power conversion apparatus is in the high frequency range.
It is also expected to minimize the size of high frequency filters and reduce the number of parts, resulting in reduced manufacturing cost of the electric power conversion apparatus.
According to a first aspect of the invention, there is provided a noise reduction device for an electric power conversion apparatus. The electric power conversion apparatus includes a converter connected to an AC power supply, a DC intermediate circuit connected to the DC output side of the converter, an inverter connected to the DC intermediate circuit and having semiconductor switching devices, and a DC smoothing capacitor connected to the DC intermediate circuit. The noise reduction device reduces a noise current caused by on and off switching of the semiconductor switching devices and flowing through the electric power conversion apparatus. The noise reduction device includes noise current detecting means for detecting the noise current and outputting a detection signal indicating the noise current; and noise-compensation-current supply means for supplying a noise compensation current for reducing the detected noise current to the electric power conversion apparatus. The noise-compensation-current supply means includes a series circuit having a current control device and a constant DC voltage supply. The output current of the current control device is controlled based on the detection signal from the noise current detecting means. The current control device exhibits a breakdown voltage lower than the voltage of the DC intermediate circuit.
Advantageously, the noise current detecting means is connected to the DC intermediate circuit to detect a common mode noise current flowing from the electric power conversion apparatus to the grounding point via the load of the electric power conversion apparatus. The noise-compensation-current supply means generates, based on the detection signal from the noise current detecting means, a current for canceling the noise current flowing through the DC intermediate circuit and supplies the current for canceling to the DC intermediate circuit.
Advantageously, the noise current detecting means is connected to the DC intermediate circuit to detect a normal mode noise current flowing between the AC power supply and the load of the electric power conversion apparatus via the electric power conversion apparatus. The noise-compensation-current supply means generates, based on the detection signal from the noise current detecting means, a current for canceling the noise current flowing through the DC intermediate circuit and supplies the current for canceling to the DC intermediate circuit.
According to a second aspect of the invention, there is provided a noise reduction device for an electric power conversion apparatus. The electric power conversion apparatus includes a converter connected to an AC power supply, a DC intermediate circuit connected to the DC output side of the converter, an inverter connected to the DC intermediate circuit and having semiconductor switching devices, and a DC smoothing capacitor connected to the DC intermediate circuit. The noise reduction device reduces a common mode noise current caused by on and off switching of the semiconductor switching devices and flowing from the electric power conversion apparatus to the grounding point via the load of the electric power conversion apparatus. The noise reduction device includes noise current detecting means having a transformer, which detects the difference between the noise current flowing through one of the power supply lines of the DC intermediate circuit and the noise current flowing through the other of the power supply lines, the noise current detecting means outputting a detection signal indicating the current difference; and a noise-compensation-current supply means for supplying a noise compensation current for reducing the detected noise current to the electric power conversion apparatus.
The noise-compensation-current supply means includes a pair of current control devices and a constant DC voltage supply or a pair of constant DC voltage supplies. First output terminals of the respective current control devices are grounded, and the current control devices control the output current thereof based on the detection signal from the transformer. The constant DC voltage supply is connected between the second output terminal of either one of the current control devices and either one of the terminals of the DC smoothing capacitor, or the constant DC voltage supplies being connected between the respective second output terminals of the current control devices and the respective terminals of the DC smoothing capacitor. The current control devices exhibits a breakdown voltage lower than the voltage of the DC intermediate circuit.
According to a third aspect of the invention, there is provided a noise reduction device for an electric power conversion apparatus. The electric power conversion apparatus includes a converter connected to an AC power supply, a DC intermediate circuit connected to the DC output side of the converter, an inverter connected to the DC intermediate circuit and having semiconductor switching devices, and a DC smoothing capacitor connected to the DC intermediate circuit. The noise reduction device reduces a normal mode noise current caused by on and off switching of the semiconductor switching devices and flowing between the AC power supply and the load of the electric power conversion apparatus via the electric power conversion apparatus. The noise reduction device includes noise current detecting means having a transformer which detects the sum of the noise current flowing through one of the power supply lines of the DC intermediate circuit and the noise current flowing through the other one of the power supply lines, and outputting a detection signal indicating the current sum; and noise-compensation-current supply means for supplying a noise compensation current for reducing the detected noise current to the electric power conversion apparatus.
The noise-compensation-current supply means includes a pair of current control devices and a constant DC voltage supply or a pair of constant DC voltage supplies. First, output terminals of the respective current control devices are connected to the input side of the converter. The current control devices control the output current thereof based on the detection signal from the transformer. The constant DC voltage supply is connected between a second output terminal of either one of the current control devices and either one of the terminals of the DC smoothing capacitor, or the constant DC voltage supply is connected between the respective second output terminals of the current control devices and the respective terminals of the DC smoothing capacitor. The current control devices exhibit a breakdown voltage lower than the voltage of the DC intermediate circuit.
According to a fourth aspect of the invention, there is provided a noise reduction device for an electric power conversion apparatus. The electric power conversion apparatus includes a converter connected to an AC power supply, a DC intermediate circuit connected to the DC output side of the converter, an inverter connected to the DC intermediate circuit and having semiconductor switching devices, and a DC smoothing capacitor connected to the DC intermediate circuit. The noise reduction device reduces a common mode noise current caused by on and off switching of the semiconductor switching devices and flowing from the electric power conversion apparatus to the grounding point via the load of the electric power conversion apparatus. The noise reduction device includes noise current detecting means including a transformer, which detects the difference between the noise current flowing through one of the power supply lines of the DC intermediate circuit and the noise current flowing through the other of the power supply lines, the noise current detecting means outputting a detection signal indicating the current difference; and noise-compensation-current supply means for supplying a noise compensation current for reducing the detected noise current to the electric power conversion apparatus.
The noise-compensation-current supply means includes a series circuit formed of a first current control device and a second current control device, and a constant DC voltage supply connected between one end of the series circuit and the DC smoothing capacitor. The first current control device and the second control device switch on and off opposite to each other based on the detection signal from the transformer. The mutual connection point of the first current control device and the second current control device is grounded. The first current control device and the second current control device exhibit a breakdown voltage lower than the voltage of the DC intermediate circuit.
According to a fifth aspect of the invention, there is provided a noise reduction device for an electric power conversion apparatus. The electric power conversion apparatus includes a converter connected to an AC power supply, a DC intermediate circuit connected to the DC output side of the converter, an inverter connected to the DC intermediate circuit and having semiconductor switching devices, and a DC smoothing capacitor connected to the DC intermediate circuit. The noise reduction device reduces a normal mode noise current caused by on and off switching of the semiconductor switching devices and flowing between the AC power supply and the load of the electric power conversion apparatus via the electric power conversion apparatus. The noise reduction device includes noise current detecting means including a transformer, which detects the sum of the noise current flowing through one of the power supply lines of the DC intermediate circuit and the noise current flowing through the other one of the power supply lines, the noise current detecting means outputting a detection signal indicating the current sum; and noise-compensation-current supply means for supplying a noise compensation current for reducing the detected noise current to the electric power conversion apparatus.
The noise-compensation-current supply means includes a series circuit formed of a first current control device and a second current control device, and a constant DC voltage supply connected between one end of the series circuit and the DC smoothing capacitor. The first current control device and the second control device are switched on and off opposite to each other based on the detection signal from the transformer. The mutual connection point of the first current control device and the second current control device is connected to the input side of the converter. The first current control device and the second current control device exhibit a breakdown voltage lower than the voltage of the DC intermediate circuit.
According to a sixth aspect of the invention, the noise-compensation-current supply means, which supplies a noise compensation current for compensating the common mode noise current, includes a series circuit formed of a first current control device and a second current control device, a first constant DC voltage supply, and a second constant DC voltage supply. The first constant DC voltage supply and the second constant DC voltage supply are connected between the respective ends of the series circuit and the respective terminals of the DC smoothing capacitor.
According to a seventh aspect of the invention, the noise-compensation-current supply means, which supplies a noise compensation current for compensating the normal mode noise current, includes a series circuit formed of a first current control device and a second current control device, a first constant DC voltage supply, and a second constant DC voltage supply. The first constant DC voltage supply and the second constant DC voltage supply are connected between the respective ends of the series circuit and the respective ends of the DC smoothing capacitor.
Advantageously, the output terminals on the side, to which a constant DC voltage supply is not connected, of the current control devices are grounded via a coupling capacitor.
Advantageously, the output terminals on the side, to which a constant DC voltage supply is not connected, of the current control devices are connected to the mutual connection point of filter capacitors connected between the input terminals of the converter.
Advantageously, the constant DC voltage supply is a zener diode.